1. Field of the Invention
This invention relates to a developing device mounted on an image forming apparatus such as a copier or a laser beam printer adopting the electrophotographic process.
2. Description of Related Art
In an electrophotographic image forming apparatus using the electrophotographic image forming process, there has heretofore been adopted a process cartridge system in which an electrophotographic photosensitive drum and process means for acting on the electrophotographic photosensitive drum are integrally made into a cartridge which is detachably mountable on the main body of the image forming apparatus. According to this process cartridge system, a user himself can effect the maintenance of the apparatus without resort to a serviceman and therefore, operability could be markedly improved. So, this process cartridge system is widely used in electrophotographic image forming apparatuses.
A process cartridge comprises at least developing means and a photosensitive drum integrally made into a cartridge detachably mountable on the main body of an image forming apparatus, and there is also a process cartridge further comprising a developer container, charging means, cleaning means, etc. constructed integrally with one another.
FIG. 16 of the accompanying drawings illustrates an image forming apparatus according to the prior art. In FIG. 16, a process cartridge 100 comprises a photosensitive drum 101 which is an image bearing member, a developing device 103, a cleaning device 105, a charging member 106 and a toner container 109 which is a developer container, all being constructed integrally with each other. The image forming apparatus also has an exposing device 102, a transferring device 104, a fixing device 107 and a feeding device 108.
The exposing device 102 applies a laser beam L conforming to image information to the surface of the photosensitive drum 101 charged to predetermined potential by the charging member 106, and eliminates charges therefrom to thereby form an electrostatic latent image on the photosensitive drum 101.
An agitating member 110 is provided in the toner container 109, and prevents the coagulation of a developer (hereinafter referred to as the toner) and also carries the toner to the developing device 103. The developing device 103 develops the electrostatic latent image on the photosensitive drum 101 by a developing sleeve 111 to thereby form a toner image. The formed toner image is transferred to the surface of a transferring material fed by the feeding device 108, and is heated and pressurized by the fixing device 107, whereby it is permanently fixed, and the transferring material is discharged out of the apparatus. On the other hand, any toner, paper dust, etc. residual on the photosensitive drum 101 after the transfer are removed by the cleaning device 105.
Now, with the higher speed of the image forming apparatus in recent years, the higher-speed countermeasure and higher durability of the process cartridge 100 have been required and therefore, the amount of toner filling a process cartridge 100 has become great and the toner container 109 itself also has become large. However, the increase in the amount of filling toner gives rise to the problem that in the conventional container construction, the rising time of the toner (reaching a predetermined charging amount necessary for development) becomes long, that is, much time is required until a proper amount of development is reached.
As shown in FIG. 17 of the accompanying drawings, the toner in the toner container 109 is charged by contacting with the developing sleeve 111, and any toner which has not been used for development returns into the toner container 109. When the amount of filling toner becomes great, the occasion on which the toner in the toner container 109 contacts with the developing sleeve 111 decreases and therefore, much time is required until all the toner in the toner container 109 reaches a predetermined charging amount.
FIG. 18 of the accompanying drawings shows the relationship between the number of formed images and the amount of toner used for development (the amount of development per unit time: M/S: mass/sheet, unit mg/cm2) when the toner container is filled with 1500 g of toner to ensure, for example, recording of 30,000 sheets. As shown, when the conventional construction of the toner container 109 was filled with 1500 g of toner, 15,000 sheets of image formation were required until a proper amount of development was reached. At this time, the toner in the process cartridge 100 circulates greatly in the toner container 109, as shown in FIG. 17.
The present invention has been made in view of the above-noted problems and an object thereof is to provide a developing device which is stable in its developing characteristic from the initial stage of use.
Another object of the present invention is to provide a developing device of large capacity which is excellent in its developing characteristic.
Still another object of the present invention is to provide a developing device comprising:
a developer bearing member; and
a developer container for containing a developer therein, the developer container having a plurality of developer containing rooms (chambers) provided with developer conveyers for conveying the developer toward the developer bearing member;
wherein the rotational speed of the developer conveyer in the room (chamber) nearest to the developer bearing member is higher than that of the developer conveyers in the other rooms (chambers).
Yet still another object of the present invention is to provide a developing device comprising:
a developer bearing member; and
a developer container for containing a developer therein, the developer container having a plurality of developer containing rooms (chambers) provided with developer conveyers for conveying the developer toward the developer bearing member;
wherein the volume of the room (chamber) nearest to the developer bearing member is smaller than that of the other rooms (chambers).
a further object of the present invention is to provide a developing device comprising:
a developer bearing member; and
a developer container for containing a developer therein, the developer container having a plurality of developer containing rooms (chambers) provided with sheet-shaped developer conveyers for conveying the developer toward the developer bearing member;
wherein the thickness of the developer conveyer in the room (chamber) nearest to the developer bearing member is smaller than that of the developer conveyers in the other rooms (chambers).
Still a further object of the present invention is to provide a developing device comprising:
a developer bearing member; and
a developer container containing a developer therein, the developer container having a plurality of developer containing rooms (chambers) provided with sheet-shaped developer conveyers for conveying the developer toward the developer bearing member;
wherein the Young""s modulus of the developer conveyer in the room (chamber) nearest to the developer bearing member is smaller than that of the developer conveyers in the other rooms (chambers).
Further objects of the present invention will become apparent from the following detailed description when read with reference to the accompanying drawings.